A display device provides a visual representation of images including text, which are acquired, stored or transmitted in various forms. Examples of display devices include, but are not limited, to computer displays, video monitors, oscilloscopes, television displays, and display panels on portable electronic devices. Display devices generally comprise a screen including an array of pixels and associated circuitry for rendering the images on the screen. Each pixel may include multiple sub-pixels, for example, red (R), green (G), and blue (B) sub-pixels, one or more of which may be shared by or among neighboring pixels. A display having R, G and B pixels is known as an RGB display.
The sub-pixels render display characteristics and features such as color, luminance, saturation, hue, brightness and other image properties of a display device. Display brightness varies with the ambient environment in which the display device is viewed. In order to display a clear image, the brightness of the displayed image must be greater than the ambient light. Display brightness may be increased by increasing power applied to the display. Display brightness may also be increased by adding a white sub-pixel to each pixel.
In an RGB display, white color is generated when all primary (RGB) color settings are at a maximum value. For example, the RGB display in an 8 bit color setting will display white color when all three primary color sub-pixels are set at a maximum value (e.g., 255 in an 8 bit setting). A display device with pixels having a white sub-pixel in addition to R, G and B sub-pixels is known as a RGBW display. The addition of the white sub-pixel increases the brightness of images with non-saturated colors. Images with fully or nearly fully saturated colors will be affected by the presence of the white sub-pixel. Areas of images with saturated colors will appear dark (or dull) since white sub-pixels cannot enhance brightness of saturated colors.
A saturated color is a color wherein one or two of the primary color setting approximates to zero. For example, in a RGB display, if only the red (R) sub-pixel has non-zero brightness, the pixel is said display saturated red color. It should be appreciated that images with non-saturated colors are statistically more common than images with saturated colors. However, the graphical user interface or displays of many portable products, such as cellular phones, commonly uses fully or nearly fully saturated colors. The addition of a white sub-pixel will generally reduce power consumption and increase the overall display brightness. However, the issue of perceived darker (or dull) saturated color needs to be addressed to better present a full spectrum of images in the presence of white sub-pixels.
Another method includes control of color information of the sub-pixels. The color information of the sub-pixels is altered to achieve a better luminance by adjusting color saturation of the sub-pixels. Alteration in the color information however changes the original colors of the image. It is generally desirable to maintain the intended color and luminance balance of an image in display devices with white sub-pixel configuration.